1. Field of the Invention
The present invention relates generally to read heads for magnetic data storage mediums, and more particularly to a read head sensor using antiferromagnetic material to fix pinned layers in the sensor.
2. Description of the Prior Art
A computer disk drive stores and retrieves data by positioning a magnetic read/write head over a rotating magnetic data storage disk. The head, or heads, which are typically arranged in stacks, read from or write data to concentric data tracks defined on surface of the disks which are also typically arranged in stacks. The heads are included in structures called “sliders” into which the read/write sensors are imbedded during fabrication. The heads fly above the surface of the disks on a thin cushion of air, and the surface of the heads which face the disks is called an Air Bearing Surface (ABS).
The major goal in recent years is to increase the amount of data that can be stored on each hard disk. If data tracks can be made narrower, more tracks will fit on a disk surface, and more data can be stored on a given disk. The width of the tracks depends on the width of the read/write head used, and in recent years, track widths have decreased as the size of read/write heads have become progressively smaller. This decrease in track width has allowed for dramatic increases in the recording density and data storage of disks.
Recent read heads typically use a tunnel junction sensor for reading the magnetic field signals from the rotating magnetic data storage disk. The sensor typically includes a nonmagnetic tunneling barrier layer sandwiched between a ferromagnetic pinned layer and a ferromagnetic free layer. The pinned layer in turn is typically fabricated on or beneath an antiferromagnetic (AFM) pinning layer which fixes the magnetic moment of the pinned layer at an angle of 90 degrees to the air bearing surface (ABS). The tunnel junction sensor is itself typically sandwiched between ferromagnetic first and second shield layers. These first and second shield layers also serve as first and second leads, and are connected to the tunnel junction sensor for conducting a tunneling current through it. The tunneling current is preferably configured to Current Perpendicular to the Planes (CPP) of the film layers of the sensor, as opposed to a sensor where a sense Current In the Planes (CIP) or parallel to film layers of the spin valve sensor. The CPP configuration is attracting more attention lately, as it can be made to be more sensitive than the CIP configuration, and thus is more useful in higher densities of tracks and data.
AFM material used to fix the orientation of the pinned layer must be in close proximity to the pinned layer and is typically fabricated on top or beneath the pinned layer. The AFM material thus contributes to the overall height of the stack of layers, and thus to the overall height dimension of the read sensor. This contribution can be substantial, as it is not uncommon for the AFM material to be as thick as the other layers combined. As discussed above, the quest in disk drive head manufacture is for reduced size. Thus, a configuration which reduces the overall thickness of the sensor by repositioning the AFM material would have significant advantages.
Also as discussed above, CPP configurations are becoming more favored for their increased sensitivity. This configuration requires that electric current be conducted through every layer of the stack. The AFM material which is included in the typical stack must therefore necessarily be conductive. However, resistance in the materials generally causes them to heat as they conduct. This heat can cause variation in the magnetic properties of AFM materials, and thus also in the pinned layer. If the AFM material were removed from the conduction path, and made of insulating materials, overall stability would be improved.
Thus there is a need for an improved configuration of read head sensor which has reduced overall dimensions, and improved stability of its magnetic properties.